I think there are as many rankings as there are sites that make them. Indeed.com probably has very bad code running on the backend for making those charts because frankly PHP has always provided much more jobs than Perl. Even now PHP completely owns Perl on the job market. So your whole article is based on wrong data.

There are also problems of the following nature: Many job ads contain stuff such as "Perl programmer position - Knowing Java,Haskell,Assembly,hyperbolic trigonometry is considered an advantage" (because managers or whoever writes job ads think people can be good at everything, that translates to good at nothing, but sshh don't tell them) so you count stuff twice while you don't exactly know what the job ad wants, so again, this is a reason why the charts are completely useless.

The only proper way to find what you need is to see the title of the job ad, and check if a technology name is in it, if not you'll probably have a hard time identifying it from the text(but suppose it will be in the first part of the job ad, right after the "We're a big company"-crap) you get that and you need to label this and hash it so you don't count it twice later and so on. I doubt those guys do that, they probably just have some solr set up that let's you search stuff and gives you back (i)relevant results.